Hitherto, there has been known a hot-water supply system having a hot-water supply apparatus of an instantaneous heating type connected in series at a downstream side of a hot-water tank unit in which water in a hot-water tank is heated by a heat pump (for example, refer to Japanese Patent Laid-open No. 2000-329401).
When the hot-water supply apparatus is connected in series at the downstream of the hot-water tank unit, a pipeline for the hot-water to flow from the hot-water tank to a tap of a hot-water supply pipe via the hot-water supply apparatus becomes long. Accordingly, a pressure loss in the pipeline becomes great, which causes a problem that a sufficient flow of hot-water may not be available.